1. Field of the Invention
The present invention relates to steam turbines for obtaining energy with use of steam, seals disposed outside the steam turbines in a rotor radial direction to suppress the leakage of steam, and methods for controlling the steam turbines and the seals.
2. Description of the Prior Art
As one effective means for improving the efficiency of a steam turbine it is known to shorten the time required for unsteady operation such as start and stop of the steam turbine.
Usually, when starting up a steam turbine, a relative rotor expansion in the corresponding cylinder caused by a difference in heat capacity between a rotor with moving blades attached thereto and a casing which houses the rotor therein is controlled by warming up the steam turbine gradually. In this way the state of the steam turbine is changed slowly up to the state of its steady operation while preventing the rotor relatively small in heat capacity in comparison with the casing from expanding to excess with respect to the casing and causing shaft vibration (rubbing vibration), and thereafter the steam turbine is started up. Thus, for shortening the time required for unsteady operation, it is necessary to solve the problem of the relative rotor expansion in the corresponding cylinder.
As a technique for diminishing the problem of the relative rotor expansion in the corresponding cylinder and shortening the unsteady operation time there has been proposed a technique wherein a heat medium flowing passage is attached to the outer periphery surface of the casing which is larger in heat capacity than the rotor, thereby heating (or cooling) the whole of the casing in advance (see, for example, JP-U-62-34103).
However, the above technique premises warming-up or cooling of the entire casing and is less effective in the case where steam necessary for warming up or cooling the casing cannot be supplied sufficiently, thus its practical application sometimes encounters difficulty. Besides, as to improving the efficiency in steady operation which is associated with shortening the unsteady operation time by preheating or precooling, no appropriate measure has been considered. Thus, it is necessary to improve the efficiency of the steam turbine from a synthetic standpoint taking a series of flows from start to stop into account.